The present invention relates generally to switches and, more particularly, to temperature responsive tip-switches.
Switches are well-known electromechanical devices which are commonly used to open and close electrical circuits.
One well-known type of switch is a temperature sensitive switch. Temperature sensitive switches, such as a thermostat, typically comprise a temperature sensor which is used to open or close electrical contacts at specified temperatures. Typically, a bimetal strip of dissimilar metals is used as the sensing element for temperature sensitive switches. The bimetal strip of dissimilar metals tends to curve upon a change in temperature due to the different rates of expansion of the dissimilar metals. The curvature of the bimetal strip is then used to open and close the electrical circuit accordingly.
Temperature sensitive switches are often used for thermal protection purposes. For example, if a device gets too hot, the temperature sensitive switch opens the electrical circuit, thereby eliminating power to the circuit.
Another well-known type of switch is a gravity sensitive, or tip-over, switch. Gravity sensitive switches, such as liquid mercury button tip switches, typically comprise a gravity sensitive element which detects movement and accordingly, opens or closes electrical contacts for the electrical circuit in response to the movement.
Switches having temperature sensitive and gravity sensitive properties, such as temperature responsive tip-switches, are well-known in the art and are commonly used to control alternating current circuits for a variety of applications. For example, temperature responsive tip-switches are particularly useful in connection with electric heaters.
In U.S. Pat. No. 3,964,004 to C. S. Mertler, there is disclosed a combined thermostatic switch and tilt switch is disclosed which is of the stack type with slow make and break contacts. A temperature responsive element such as a bimetal actuates a set of contacts and an attitude responsive means such as a swingable pendulum also actuates a set of contacts. These two responsive means may actuate the same set of contacts or may actuate different sets of contacts in various embodiments of the invention, but a second set of contacts is provided in the switch as a standby set of contacts which may be actuated by one of the responsive means in the event that the first set of contacts fails to be actuated, e.g. by being welded together or some other malfunction.
Temperature responsive tip-switches are highly desirable because a single switch provides both temperature and gravity responsive interruption for an electrical circuit. As a consequence, temperature responsive tip-switches can considerably reduce the overall size and cost to manufacture the device which utilizes the temperature responsive tip-switch.
It should be noted that temperature responsive tip-switches of the type described above often experience a notable drawback. Specifically, temperature responsive tip-switches of the type described above typically comprise a slow-action thermostat which uses slow make and break constructions to open and close its electrical contacts. As a result, the switching process can be relatively slow, which can be undesirable due to the possibility of excessive contact arcing resulting in reduced contact life and radio noise interference.